This invention relates in general to gas decomposition and to a new and useful method and apparatus for the decomposition of a multicomponent gas such as air.
The invention concerns a device for the decomposition of a multicomponent gas, especially air, and the concentration of at least one component thereof. A gas supply line connects a gas source with a separation forechamber, from which a product gas enriched in at least one component of the gas can be removed. The gas is removed across a product gas line. From the product gas line the waste gas, which is depleted in the particular component, can be sent across a branch line to a subsequent secondary separation chamber, from which a secondary product gas can be removed across a secondary product gas line.
A similar device is known from EP-A No. 91 969. The known device is used to produce a highly pure gas, hydrogen in the familiar application, which is to be cleaned of its unwanted impurities. For this, the feed gas is supplied to a separation forechamber, configured as a permeation chamber, which is equipped with a hydrogen-permeable membrane. The supplied impure gas enters the retentate chamber. From here, primarily the hydrogen component crosses the membrane to the permeate chamber, so that the gas is cleared of most of the impurities and hydrogen is present in the concentrated state. The impurities left behind in the retentate chamber are sent on or later use across a product gas line. The thus precleaned hydrogen is sent from the permeate chamber across a branch line to an alternating pressure adsorption bed, being a secondary separation chamber, in which the spent gas from the permeation chamber is cleared of the remaining impurities.
A disadvantage of the familiar device is the fact that, because of the successive connection of first the permeation chamber and then the alternating pressure adsorption bed to the same feed gas line, the pressure losses of both separation chambers are added. Therefore, the pressure in the permeate chamber is to be maintained at least high enough for efficient operation of the following alternating pressure adsorption beds. If the feed gas pressure is low, such as 1.5 to 5 bar, there are no longer sufficient pressure reserves to operate the adsorption bed, the reason being a pressure reduction between the feed gas line and the branch line of the permeation chamber by a factor of around 2-5. If the familiar device is operated with such low feed gas pressures, the gas pressure would have to be raised again to a suitable level prior to entering the alternating pressure adsorption beds. This could be done e.g. with a compressor, but the overall layout would become more expensive, costly, and heavy.
The efficiency of the permeation chamber, moreover, depends not only on the pressure ratio between the retentate chamber and the permeate chamber on either side of the permeable membrane, but even more on the partial pressure ratio of the component being concentrated on either side of the membrane. In the case of the known device, this partial pressure ratio is not adjustable, but instead results from the pressure and concentration relationship prevailing in the permeation chamber during the operation.